Added cursor.description convenience and cursor.fetchmany

[WilliamStam]

cursor.description

by the looks of it it should be available as cursor._cursor.description but anyways.. this is purely for convenience

see somone else was looking for this https://github.com/GoodManWEN/cx_Oracle_async/issues/19

cursor.fetchmany

fetchone, fetchall, fetchmany are the main function calls on the db handlers. just to bring this cool project in line with those... (the fact that i needed it has noooothing to do with it :P) i added this in

use case (fetch 2 rows at a time as a dict):

await cur.execute(query)
desc = [d[0] for d in  cur.description]
while True:
    rows = await cur.fetchmany(2)
    if not rows: # no rows left so we done
        break
    for row in rows: 
        print(dict(zip(desc, row))) # this is a dict of each row now

[WilliamStam]

i have no clue why pycharm changed any of the other lines :( only things i added in are

@property
    def description(self):
        return self._cursor.description

and

async def fetchmany(self, *args, **kwargs):
    # block mainly happens when fetch triggered.
        return await self._loop.run_in_executor(self._thread_pool, self._cursor.fetchmany, *args, **kwargs)